The invention relates to a method for recrystallization of layer structures by means of zone melting, in which, as a result of convenient arrangement of a plurality of heat sources, a significant acceleration of the zone melting method can be achieved. The method is based on the fact that a continuous recrystallisation of the layer is ensured as a result of overlaps being produced. According to the invention, a device is likewise provided with which the method according to the invention can be achieved. The method according to the invention is used in particular in the production of crystalline silicon thin layer solar cells or for example in SOI technology. However the application likewise relates also in general to the processing of metals, plastic materials or adhesives and here in particular to the production of thin layers.
The production of thin doped semiconductor layers for electronics and photovoltaics is at present implemented in the most varied of ways. In general, the aim is to produce sandwich-like layer structures comprising differently doped partial layers. Typically, a plurality of process steps is thereby used which construct the layer structures sequentially. For solar cells made of crystalline silicon, the crystal structure is of fundamental importance for the degree of effectiveness which can be achieved. The fewer the defects in the crystal, the simpler is the production of highly efficient solar cells.
The state of the art in the field of semiconductor structures are methods in which the semiconductor is recrystallised after a deposition step again via the liquid phase in order to change for example the crystal structure. Such an application is provided for example in “Silicon on Insulator” (SOI) Technology or also in the field of crystalline silicon thin layer solar cells.
Crystalline silicon thin layer solar cells are being researched at present in different concepts. One of these concepts is represented by way of example in FIG. 1. For the production of a solar cell represented in FIG. 1, the manufacturing steps represented in FIG. 2 are required. The method step for recrystallisation of the layer via the liquid phase, represented in FIG. 2, can be implemented by means of various methods. One of these methods is zone melting (zone melting recrystallisation, ZMR). The nucleus layer represented in FIG. 1 is heated by a linear or linearly scanned heat source such that it melts linearly over the entire width of the substrate. This molten line, i.e. the melting zone, is drawn by a relative movement of substrate and heat source in the direction perpendicular to the melting zone in the substrate plane through the entire substrate length.
As a function of the drawing speed and the temperature gradient at the melting zone limits, crystals are produced which are extended in the drawing direction and have different dimensions. It is a typical aim of each zone melting process to produce crystals which are as large and as low in defects as possible. However in the case of using a zone melting process for photovoltaics, this aim runs counter to economical target specifications for a cost-effective process. From the point of view of economics, the throughput must be as high as possible, i.e. at least 0.1 m2/min, the high crystal quality which is possible at moderate drawing speeds being intended to be maintained simultaneously.